The invention relates to a method for a firm bonding of a first material with a second material by means of soldering through focused laser radiation impacting on the first material whose output is controlled in dependence of the temperature measured through heat radiation emitted by the first material in the direction of the laser radiation. The invention also makes reference to an arrangement for the soldering of a first material onto a second material comprising a laser source emitting a laser radiation; a first optics focusing the laser radiation onto the first material; a sensor that, via the first optics, registers the heat radiation emitted by the first material as measuring radiation; as well as a beam splitter via which the laser radiation from the beam path of the measuring beam path or the measuring beam path from the beam path of the laser radiation can be deflected.
Lasers, in particular fiber-coupled lasers, may be used for soft-soldering connectors such as copper strips onto solar cells in order to interconnect them to form solar modules. According to the state of the art, the laser radiation is first collimated and combined with the beam path of a pyrometer in order to focus the sensor of the pyrometer and the laser spot coaxially onto the copper strip. In this context, laser and pyrometer form a closed servo loop. In this case, a chronologically adjustable set-point temperature will be specified. A controller adjusts the laser output in such a way that the set-point temperature will be attained as closely as possible. In this case, laser spot and measuring point will coincide. This results in the disadvantage that the laser radiation may influence and distort the pyrometer measuring. For example, absorbing or poorly heat conducting materials may be imbedded on the surface of the copper strips, such as dust, flux materials, oxides. Therefore, the laser radiation may generate sparks or other local heat sources on the surface that, however, do not reflect the temperature of the material itself.
These influences leading to measuring errors occur in particular within the temperature range of soft soldering since highly sensitive pyrometers are used for low temperatures.
A method forming its own generic category can be found in DE-A-100 64 487. In order to control the output of the laser beam, the temperature at the point of impact of the laser on the soldering spot is measured contact-free. To this end, a radiation pyrometer is integrated into the laser beam source.
The subject of DE-A-10 2004 050 164 is a welding method by means of laser radiation. In order to measure the amount of energy entered for controlling the output of the laser radiation, the temperature on the side of the material to be welded lying opposite the welding spot is measured by means of a pyrometer.
From EP-A-1 477 258, a device and a method for local temperature treatment with a heat detector and image processing have been known. In this case, the temperature at the point of impact of the laser radiation on an object is measured by means of a pyrometer. The heat radiation to be measured is decoupled from the laser radiation as reradiation.